Soil shear testing machine



Oct. 27, 1953 T. R. DAMES ET AL I son. SHEAR TESTING MACHINE l t e e h 4 s t e e h s 4 1 Filed Feb. 19, 1949 w kl Qii INVENTORS 725/47 Q. DHMES BY JOHN 0. MHLONEV ORNEY.

Oct. 27, 1953 T. R. DAMES ET AL 2, ,718

SOIL SHEAR TESTING MACHINE Filed Feb. 19. 1949 14 Sheets-Sheet 2 INVENTORS 726 /7 2. 095465 w/L L/flM (1/- M0026 BY JOHN a}. MflLO/JEV WHEY.

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SQIL SHEAR TESTING MACHINE 14 Sheets-Sheet 4 Filed Feb. 19, 1949 INVENTORS 725m e. a ua-s w/u/mw 11/. M0025 BY JOHN w. MflLO/IEV Oct. 27, 1953 t T. R. 'DAMES ET AL 2,65

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T. R. DAMES ET AL SOIL SHEAR TESTING MACHINE Oct. 27, 1953 14 Sheets-Sheet 6 Filed Feb. 19, 1949 mmu N2. u

' INVENTORS TEE/47' DHMES 5 WW W wM mw LN n m 6 5 ATTORNEY.

T. R. DAMES ET AL SOIL SHEAR TESTING MACHINE l4 Sheets-Sheet '7 INVENTORS M55 M0026 ONE A ORNEY.

Oct. 27, 1953 Filed Feb. 19, 1949 TRENT E- OF? WILL/HM 60. BY JOHN w. M!

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son SHEAR TESTING MACHINE 14 Sheets-Sheet 9 Oct. 27, 1953 Filed Feb. 19, 1949 Oct. 27, 1953 T. R. DAMES ET AL SOIL SHEAR TESTING MACHINE l4 Sheets-Sheet 10 Filed Feb. 19. 1949 mam man Mom INVENTORS WENT Q. DWES WILL/HM (U- MOORE New BY JOHN (U. MfllO/VEV TORNEY.

Oct. 27, 1953 T. R. DAMES ET AL 2, ,718

SOIL SHEAR TESTING MACHINE Filed Feb. 19. 1949 14 Sheets-Sheet ll SIG E wil -K590 455 I SIS INVENTORS TEENT IQ. DflMfS tU/LL/flM CU- MOORE QZM/ y JOHN 6U. MHLONE'V Oct. 27, 1953 "r. R. DAMES ET AL SOIL SHEAR TESTING MACHINE l4 Sheets-Sheet 12 Filed Feb. 19, 1949 566 ea 6% m m 57c;

sea 59m- INVENTORS TEEHT e. DHMES w/LLIflM w. 4400/? BY JOHN (U. MQLOHE WTTOENEV Oct. 27, 1953 T. R. ijAMEs ET AL 2, 56,718

son SHEAR TESTING MACHINE Filed Feb. 19. 194 ,14 sheets-sheet 1s RELEASE GIS RHEOSTHT INVENTO s TRENT e OflME' w/ u/mw w. MOOQE y JOHN w. M/JLOHEV rroeuEs Oct. 27, 1953 T. R. DAMES Er AL I 2, ,7

SOIL TESTING MACHINE Filed Feb. 19, 1949 '14- Sheets-Sheet 14 O m IN VEN TORS o TRENT e. DflMES w/LL/flM w. MaoeE y JOHN w. MHLONEV I l E I Patented Oct. 27, 1953 SOIL SHEAR TESTING MACHINE Trent R. Dames, San Marino, William W. Moore, San Francisco, and John W. Maloney, Alhambra, Calif.

Application February 19, 1949,Serlal1No. 77,382

29 Claims. 1

The presentinvention relatesto materials testingmachines, and more particularly to a machine for determining the shearing strength of soil samples taken from different locations and depths at the site of a proposed structure, or for ascertaining the frictional values of soil against some other material, so that accurate and reliable data can be formulated as to the load-bearing-capacity or slidingcharacteristics of the soil. Such information is essential in setting up: the design specifications of structural foundations, and enables the structural engineer to utilize the maximum economies in the foundation design without jeopardizing the integrity of the structure.

The shearing strength and frictional values'of' soil samples are useful also in determining the safe loading for driven piles, as described in the Dames and Moore Patent 2,296,466, September 22, 1942, entitled Method of Determining Driven Friction Pile Capacities, as well as in other analyses of the loading and pressur conditions obtained on retaining walls, quay walls, bulkheads, and the like. The stabilityv of soil bodies such. as earthen embankments and fills, or the sides of excavations, can also be determined accurately when the shearing strength and frictional values of the soil are known; and the sliding characteristics of the sides of a out can be analyzed to ascertain the factor of safety. Another importantuse to which such information can be put is in determining the strength of a sub-grade, so that the minimum required thickness for pavement can be established.

While the present invention isprimarily concerned with the testingof soils, we wish tomake it clear that the machine isnot limited solely to such use, but might also be employed in the testing of other materials having shearing and frictional properties. generally similar to those of soil, such as sugar or borax, for example, both of which have already been tested in connection with problems relating to the design of bins and hoppers.

The soil samples to be tested are cylindrical cores which are contained withinthree adjoining, separable rings; such samples being usually obtained with any suitable core sampling device, such as the preferred type shown and described in Dames Patent 2,318,062, granted May 4, 1943. The sampler of the patent is in the nature of a hollow tubular body having a sharp cutting edge at the bottom end thereof, with a. plurality of thin-walled core retaining rings containedwithin the body. The, sampler is driven into the ground,

7 usually at thebottom ofa bore, and when withthroughout the test.

2 drawn, lifts the cores with it. They core retaining rings are then removed from the body, and separated intosections of three ringseach; each of said 3-seg ment sections forming a single sample for use in the present machine.

Among other factors, the shear strengthof. the soil ata given point is a function of the natural underground soil. pressure prevailing at that point; hence, for a given type'of soil, the greater the depth below the surface, the greater is. the pressure, and the higher the shear strength. In order to obtain an accurate shear strength value for a given soil sample, it is, necessary therefore to apply a surcharge or compression force to the specimen accurately duplicating the natural underground soil pressure existing at the site from which the sample was taken, or simulating the anticipated pressure atthe site under con-v sideration.

One of the problems encountered in the-design of a surcharging mechanism is that of maintaining th surcharge force at a constant value For example,,it is not uncommon for a soil sample to give or compact slightly after being held under load for some time, which causes an appreciable shortening in. the length of thesample, with acorresponding reduction in the applied surcharge pressure unless suitable provision ismade for follow-up. Or, during the shearing of the sample, the relative sliding movement of the grains. in the movable segment over the grains in the stationaryxsegment. may cause a slight expansion in the length of the sample,,with an attendant increase in the surcharge pressure unless suitable provision is made to accommodate such expansion. Any variation in the surcharge pressure during the progress of a test has an adverse effect upon the results obtained, and. unless the deviation in surcharge pressure is noted and corrected, the values obtained will be in error and therefore unreliable.

One of the objects of the present invention is to overcome the. aforementioned difiiculty by providing means for automatically maintaining the surcharge pressure at a constant value at all times. This object is attained by providing. a reversible electric motor which applies the surcharge pressure to the soil sample through the medium of a lead screw and spring arrangement, and which is actuated by two limit switches mounted on one of the two spring-separated members at one end of the sample. Anadjustable screw on the other of the said members is operative to actuate one of the two limit switches when the springs have been compressed by a predetermined amount, so as to stop the motor. If, during the course of the test, the sample should expand longitudinally due to the aforementioned slippage of the grains of soil, causing the surcharge pressure to increase, the other limit switch is actuated by the adjustable screw, causing the motor to operate in reverse until the excess pressure has been relieved and the surcharge pressure has been restored to the predetermined value. Amon the advantageous features of the invention is the fact that the surcharge pressure is applied symmetrically to both ends of the sample, instead of to one end only, as in certain prior machines known to applicants.

Another object of the invention is to provide a materials testing machine of the character described, having a novel and improved mechanism for producing shearing deflection of the sample, and for exerting the shearing load force on the sample. In the preferred form of the invention illustrated in the drawings, this shearing deflection and load mechanism embodies a control member in the form of a floating shear box which is supported for free sliding movement in a direction perpendicular to the axis of the sample. Mounted within the shear box is a reversible electric motor, known as the shearing deflection motor, which drives a gear member having a screwthreaded connection with a screw shaft that is attached to the center ring holder of the soil sample. The axis of the screw shaft is disposed parallel to the direction of travel of the shear box, and as the motor-driven gear member turns on the shaft, the latter is moved longitudinally to produce shearing deflection of the center ring of the sample with respect to the outer rings thereof. Such longitudinal movement of the screw shaft causes the shear box to tend to be pulled toward the sample, and this tendency is resisted by the shearing load mechanism which exerts a spring force on the shear box substantially equal and opposite to the force exerted by the screw shaft, so that the shear box is maintained in a substantially fixed position.

The shearing load mechanism includes a heavy load spring which is fastened at one end to the shear box on the side opposite the sample. The other end of the load spring is attached to a spring carriage mounted on a pair of lead screws that are driven by another reversible electric motor, Known as the shearing load motor, and when this motor operates in the forward direction, the spring carriage is moved in the direction to stretch the load spring, thereby exerting a shearing load force on the shear box. A pair of oppositely facing, automatic control microswitches mounted on the movable shear box are engageable by limit stops on the stationary structure of the machine as the box moves in one direction or the other, causing one or the other of the two motors to operate automatically in the forward or reverse direction, as the need may be. Thus, if the machine is set up so that the shearing deflection motor runs continuously or intermittently in the forward direction, the movement of the shear box toward the sample responsive to such motor operation causes one of the automatic control microswitches to be actuated, which starts up the shearing load motor, thereby exerting a force on the shear box tending to return the same to its original position.

Another object of the invention is to provide a materials testing machine having automatically controlled means for increasing by predetermined increments either the shearing deflection of the sample or the shearing load applied thereto. This object is realized by the provision of an automatic timer which sends out momentary current impulses at predetermined intervals of time; together with an electrical circuit including relays which are actuated by the aforesaid current impulses to start up and operate either the shear motor or the load motor. These relays are disabled to stop the associated motor when the shearing deflection or shearing load has been increased by a predetermined increment, and this is accomplished by suitable cam means in the mechanism operating microswitches which break the circuit to the coil of the relay involved.

A further object of the invention is to provide a materials testing machine which can be set up to operate under any one of the following four test procedures: (1) shearing load increased by predetermined increments applied at predetermined intervals of time, with the shearing deflection increased by the operation of automatic controls at a rate such that the resistance to deflection balances the load; (2) shearing deflection increased by increments, with the shearing load increased by the operation of automatic controls to balance the resistance of the sample to deflection; (3) shearing load increased continuously and at a substantially uniform rate, with the shearing deflection increased 'by the operation of automatic controls; and (4) shearing deflection increased continuously and at a substantially uniform rate, with the shearing load increased by the operation of automatic controls to balance the resistance of the sample to deflection. It will be seen that in the first and third cases, shearing load is imposed as an independent variable, and deflection follows as a dependent variable; while in the second and fourth, deflection is the independent variable, and load is the dependent variable. The advantage of being able to run a test by any one of the procedures enumerated above is that it enables the engineer to select the type of test indicated for the particular type of loading condi-- tions anticipated in the soil under consideration. Another advantage is that the results obtained by one test procedure can be compared with those obtained by the other procedures, and with other test data compiled by other investigators using any one or more of these methods, so that the ultimate findings will represent reasonable conclusions based upon a comprehensive collection of data derived from many sources and obtained by many different testing techniques.

Still another object of the present invention is the provision of a novel and improved recorder mechanism for accurately recording the surcharge vs. shearing load and deflection vs. load relationships obtained in the sample during the progress of the test. In its preferred form, the recorder mechanism of the present invention comprises two longitudinally spaced units which extend across the top of the machine transverse to the direction of travel of the load spring carriage. Each of these units consists of an endless bronze tape trained around two pulleys, and mounted on the tape are three stylus carriers. The two recorder units are disposed directly above a sheet of coordinate paper attached to a data board mounted on the spring carriage, and these units are tilted about their longitudinal axes so that the lower straight edge of each unit is spaced closely adjacent to the surface of the coordinate paper. As the stylus carriers travel along this lower edge of the unit, the springretracted stylus pins associated therewith are en- '5 gaged and pressed downwardly at predetermined time intervals by a vertically movable, solenoidactu-ated striker bar, causing the pins to make dots on the sheet of coordinate paper. The pulleys of the recorder units are shaft-driven from the power transmission systems driving the surcharge lead screws and the shearing deflection screw shaft, respectively; hence the position of each dot formed by the stylyus pins is av function of the distance traveled by the spring carriage, and the amount by which either the screw shaft or the surcharge lead screw has advanced from its initial position. Thedistance traveled bythe spring carriage gives the tension of theshearing load spring, while the advance ofthe screw shaft and surcharge lead screw denote the shearing deflection and surcharge pressure, respectively. The time factor in the test is also represented graphically by the spacing between dots, inasmuch as the dots are made at predetermined time intervals.

The foregoing and other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment thereof, reference being had to the accompanying drawings, wherein:

Figure 1 is a top plan view of a machine embodying the principles of the invention, the cover plate of the machine being removed to expose the internal mechanism thereof;

Figure 2 is a partially sectioned side elevational view of themachine, taken along the line 2--2 of Figure 1;

Figure 3 is an enlarged longitudinal vertical section, taken along the plane 3-3 in Figure 1;

Figure 4 is a sectional view of a detail, taken at 4-4 in Figure 3;

Figure 5 is an enlarged sectional view, taken at 5-5 in Figure 3, showing the surcharge mechanism in front elevation;

Figure 6 is a transverse section through the surcharge mechanism at 66 in Figure 3;

Figure '7 is an enlarged sectional view, taken at l--'I in Figure 6, showing the internal mechanism of the limit switch box;

Figure 8 is a horizontal sectional view through the machine, taken along the plane 88 in Figure 3;

Figure 9 is a vertical section through the shear box, taken at 9-9 in Figure 3;

Figure 10 is a transverse vertical section through the machine, as seen along the section line Hll in Figure 1;

Figure 11 is anothervertical section, looking in,

the other direction from H-I I in Figure 1;

Figure 12 is an enlarged sectional view, taken at l2-l2 in Figure 1;

Figure 13 is a section taken at |3-|3 in Figure 12; showing the inked ribbon drive mechanism in one of its two operating positions;

Figure 14 is a view similar to Figure 13, but showing the mechanism in the other position;

Figure 15 is an enlarged sectional view through the recorder mechanism, taken at l--l5 in Figure 1;

Figure 16 is a sectional view through one of the recorder units, taken at [6-46 in Figure 15; showing one of the stylus carriers at the point of. leaving the inked ribbon at one end of the device, and another stylus moving into operative position over the ribbon at the other end thereof;

Figure 17 is a view similar to Figure 16, but showing the stylus holdersin another position on the recorder unit;

Figure 181i$- a. top plan view. of the timer mech-- anism. for. transmitting momentary current impulses to the machine at predetermined intervals of timev to actuatethe motor-starting relays when increasing. the shearing deflection orload by increments, and for actuating the recordersolenoids;

Figure 19 is a vertical section through the same, along line. lee-l9 of Figure 1.8;

Figure 20-is a front elevational view of the control panel for the machine, with a schematic representation of the associated electrical circuit superimposed thereon; and- Figure. 21 is a schematic diagram of the circuit in themachineitself.

In the drawings. the machine will be seen. to comprise a housing 25 which encloses the operating. mechanism, and which is supported, on a stand 26 formed of horizontal channel beams 21 that are bolted or. otherwise secured to thetop end of four legs 28 located. at the corners of the machine. The housing 25' consists of a horizontal bottom plate 29 resting on and secured to the channels 2! of the supporting frame, together with end plates 30 and 31, front platev 32, back plate 33 and top plate 3.4. The bottom plate 29 and left-hand end. plate 30 are preferably made of metal, but the top plate 34-, right hand end plate 31, and front and back plates 32.. 331 may be made ofv transparent plastic, if desirechso that the mechanism inside. the machine can be observed during the performance of. a test.

The mechanism contained within the housing 25 maybe grouped into four primary, units: the surcharge mechanism. 40. which has the function of applying a surcharge, or endpressure on the sample; theshearing deflection mechanism 4|, which is contained within a floating shear box 42 and produces a lateral displacement of the center section of: the three-segment sample, perpendicular to the axis of the sample; the shearing load mechanism. 43, which functions to apply a load on the floating shear box 42 balancing the resistance of the sample to shearing deflection; and the recorder unit 44, which records the shearing deflection vs. load and surcharge vs.load"relationships obtained in the sample during the performance of the test.

The surcharge mechanism 40 will be taken up first, and is seen to occupy a chamber. 45 atthe right hand end of the housing 25, between the end wall 31 and a vertical, heavy steel plate partition 46 extending from the front wall of the machine to the rear wall thereof. Entrance to the chamber 45 for the purpose of inserting a soil sample into the holders of the machine is provided by a removable panel 41 in the end wall-3|, said panel engaging and closin a. microswitch 48 which is serially connected into the electrical circuit of the machine so that the mechanism cannot be operated unlessthe panel is in place. The microswitch 48 is mounted on a bracket 49, andthe latter is secured tothe partition 46 near the topedge thereof.

The soil sample, designated by the reference numeral 50, is cylindrical in shape and is tightly confined within three adjoining-ring segments 5 I, 52 and 53 which are separable from one another. The outer rings 5| and 53 areclamped between stationary holders 54 and cooperating caps 55, while the center ring 52 is clamped between a movable holder 56- and its cap 51. Eachv of the caps 55 and 51: is secured to its respectiveholders by means of-two stud bolts 611 which project from theface of the holder, on: opposite sides of the rings. The caps are drilled to receive the studs 60 and are provided with quick-detachable locks in the form of swing clips 6| which are pivotally connected to the cap for swinging movement between the locked position, shown in Figure 3, and an unlocked position at 90 thereto.

To effect the locking action, the swing clips 6| are provided with pivot shafts 62 which are journaled in bores within the caps, said bores intersecting the edges of the drilled passageways that receive the studs 60. At the point of intersection with the passageway, each of the shafts 82 is cut out to provide clearance for the stud 80 when the swing clip 6| is swung out to the unlocked position. When the clip is in the locked position, the pivot shaft 62 seats in a semi-cylindrical recess formed in the side of stud 60, as shown in Figure 3, thereby preventing the cap from being withdrawn from the stud. This arrangement enables the three caps to be secured quickly to their holders when the sample is placed in the machine, and to be removed quickly when the test has been completed.

The two outer holders 54 are supported on the partition 46 and are secured thereto by two bolts 64 (Figure 8) cooperating with a back plate 65 and two laterally spaced front plates 66 and 61. Back plate 65 is bolted or otherwise suitably secured to partition 46, while the two front plates 66 and 67 are attached by screws 68 (Figure 4) to the back sides of the two outer holders 54. Bolts 64 pass through horizontally elongated slots in plate 65, and are threaded into tapped holes in the plates 66, 67; the back side of the plate 65 being recessed at H (Figure 8) to provide clearance for the heads of bolts 64.

A limited amount of free lateral movement of the outer holders 54 parallel to the axis of the soil sample is provided for by ball bearings I2 which are confined between two pairs of straight, horizontally extending, closed-end races 73 and I4 (Figure 4) formed in adjacent faces of the back plate 65 and front plates 66, 61. The bolts 64 are drawn up only sufficiently tight to prevent undue separation of the front plates 66, 61 from back plate 65, which would permit the ball bearings T2 to escape from their races. As tension is applied to the center holder 56, the two outer holders 54 are pulled toward the partition 46, causing the races in the plates 66, 6! to bear tightly against the ball bearings 12. The slight movement of plates 66, 61 to the left (Figure 8) causes the heads of the bolts 64 to move away from the plate 55, so that the plates 66, 61 with their attached holders are free to roll on the ball bearings E2 within the limits of the slots I0. This arrangement permits the two outer holders 54 to move apart from the center holder 56 if the sample should expand during the shearing deflection of the test, and friction of the soil against the outer rings 5|, 53 is too great to allow the soil to slide freely within the rings.

The surcharge pressure is applied to the ends of the soil sample 56 by means of two porous stone disks 30 which are slightly smaller in diameter than the inside dimension of the rings 5|, 53 so as to be freely slidable therein. The stone disks 60 are seated within recesses 8| in end plates 82, and the latter are provided on their outer faces with raised central bosses having sockets formed therein, into which bearing balls 83 are pressed. The bearing balls 83 are engaged by the projecting ends of threaded studs 84 which are screwed into tapped holes 85 in spring plates 86. Each of the studs 84 has a conical socket formed in the outer end thereof, into which the ball 03 seats. This flexible ball joint between the stud 84 and end plate 82 provides a universal connection therebetween, enabling the stone disks to accommodate themselves to any unsymmetrical consolidation of the sample. Lock nuts 81 secure the studs 84 in adjusted position.

Both of the spring plates 88 are slidably mounted on two vertically spaced, horizontally extending lead screws 90 and 9|, the ends of which are journalled in bearings 92 and 93 mounted on a partition 89 and end wall 33, respectively. The center portions of the lead screws 90, 9| are smooth-surfaced, and the spring plates 86 are provided with hearing holes 94 and 95 which slidably receive the shafts. Each of the lead screws 90, 9| is provided at one end with a right-hand thread 96, and at the other end with a left-hand thread 91, and mounted on these threaded portions are screw plates 99 and I00. It will be noted in Figures 5 and 6 that the bottom lead screw 9| has the right-hand thread 96 and the left'hand thread 91 at the right and left ends thereof, respectively, while the top lead screw 90 has the order of the threads reversed. Thus, the thread 96 at the left end of lead screw 98 is opposite to the corresponding thread 91 at the left end of lead screw 9|, and the same relationship exists at the right end of the two lead screws.

The two screw plates 99, I00 are disposed parailel to their respective spring plates 86, and are provided with threaded holes I0| and I02 that receive the threaded portions of the shaft. Each of the screw plates 99, I00 is operatively connected to its associated spring plate 86 by two compression coil springs I03 and I04, which encircle the lead screws 90, 9|, respectively. The ends of the springs I03, I04 are ground off flat, perpendicular to the axes of the spring coils, and are seated within annular channels I05 formed in the adjacent faces of the spring plates and screw plates 99, I00.

The two lead screws 90, 9| are driven in opposite directions to advance the screw plates 99, I00 inwardly toward their respective spring plates 86, thereby compressing the springs I03, I04. It is this pressure of the compressed springs acting against the spring plates 86 that is applied to the sample 50 as the surcharge, and the amount of pressure exerted thereon depends upon the amount of deflection of the springs. The lead screws 90, 9| are driven by a reversible electric motor I06 which operates through a speed reduction and right-angle-drive gear box IIO to turn a vertically disposed drive shaft I II that is journalled adjacent its ends in bearings |I2 mounted on the back wall 33. As will be noted in Figures 1 and 3, the lead screws and 9| are offset laterally with respect to one another, and the drive shaft III extends upwardly between them, passing to the left of lead screw 9| and to the right of lead screw 90 (Figure 3). Fixed to shaft III in the horizontal planes of the lead screws 99 and 9| are worm gears H3 and H4 which mesh with gears H5 and H6, respectively, on lead screws 90 and 8|. The teeth of both worms H3 and I It lead in the same direction, and lead screws 90 and 9| are therefore driven in opposite directions at greatly reduced speed from the drive shaft I I I.

The surcharge pressure on the soil sample is controlled automatically by means of a limit switch box I20 mounted on the back of the lefthand spring plate 86 (Figures6 and 7), and con tained within this box are two microswitches I2I and I22 which control the forward and reverse circuits of the motor I06. Switch I2I is normally closed, and is connected through one pole of a two-pole impulse relay I H (see electrical circuit diagram in Fig. 21) to the coil of a relay H8 which controls the forward drive circuit of the surcharge motor I06. When switch I2I is opened, relay H8 is disabled, breaking the forward drive circuit to the motor I06 and causing the latter to stop. Switch I22 is normally open,

and is connected to another relay I I9 which controls the reverse drive circuit of the motor I06. When switch I22 is closed, the relay H9 is energized, closing the reverse drive circuit of the motor I06 and causing the latter to start up in reverse.

The open outer end of the box I is closed by a cover plate I23 having inwardly directed end portions I24 which terminate in knife edge I25. The cover plate I23 is disposed between the side walls of the box I20, and the knife edges I25 bear on the recessed outer edges of the end walls I25 of the box. Bolts I21 which secure the box to the face of the spring plate 86 pass through enlarged holes I in the end portions I24 of the cover plate, and disposed between the heads of the bolts and the outer surface of the cover plate are soft rubber washers I3l. The combination of the knife edge supports I25, clearances provided for bolt I21 by the enlarged holes I30, and the resilient washers I3I between the cover plate and the heads of the bolts permits the end portions I24 of the cover plate to rock slightly, thereby enabling the center portion of the cover plate I23 to bow inwardly under the pressure of an adjusting screw I32. Intermediate its ends, the cover plate I23 is cut away leaving a rela tively thin center portion I 33 which deflects as a beam under the pressure of the screw I32. The end of the screw I32 is rounded off to obtain a substantially point contact with the cover plate I23 at the midpoint of the latter.

Formed integrally with one end portion I24 of the cover plate are two laterally spaced fingers I34 and I35 extending lengthwise of the cover, the free ends of said-fingers being adapted to engage the operating plungers I36 of the microswitche I2! and I22. The clearances between the ends of fingers I34, I35 and their respective operating plungers I 36 are regulated by means of two adjusting screws I40 which are threaded into holes in the cover plate adjacent the attached ends of the fingers, said screws engaging the fingers to bend the same inwardly toward the microswitch plungers. Finger I35 is offset, or bent outwardly, as shown to an exaggerated degree in Figure 7, so that its plunger I36 is not engaged until after the other plunger has been engaged by spring finger I34, the reason for which will presently be explained.

The spring fingers I34 and I35, being attached to the rockable end portion I24, and being further backed up by the adjusting screws I 40, tend to swing inwardly at their free ends when the cover plate is bowed in by the pressure of screw I32. Due to the offset in finger I35, the operating plunger of niicroswitch I2I is engaged and depressed first by finger I34, opening relay H8 and bringing the motor I06 to a stop. Further inward deflection of the cover plate due, for example. to endwise expansion of the sample, causes the operating plunger or microswitch I22 to be depressed by finger I35, thereby actuating relay H9 and starting motor I06 in reverse.

10 Such reverse operation of the motor continues only until the plunger of microswitch I22 is released by finger I35, at which point, the motor stops while the plunger of micro'switch I2l is still depressed by finger I34.

The adjusting screw I32 is screw-threaded through a tapped hole MI in the left hand screw plate 99 (Figure 6) and asses freely through holes I42 and I43 in walls 89 and 32, respectively. A knurled surcharge adjustment knob I44 is fixed to the outer end of the adjusting screw I32, which enables the operator to turn the screw so as to advance the same through the screw plate 99. The smooth-surfaced portion of the screw I32 passes through the hub I45 of a gear I46 and is keyed or splined to said hub for non-rotative sliding movement relative thereto. Gear I46 meshes with one of two trains of gears, designated collectively by the reference numeral I50, which are organized and. arranged to drive dials I5I, I52, I53 and I54, as well as rotatable index rings I55 and I56 which surround dials I53 and I54, respectively. Dial I5I gives the surcharge pressure in thousands of pounds, ranging from zero to 16,000, while dial I52 gives divisions of the surcharge pressure in hundreds of pounds, ranging from zero to 1,000. Dial 'l53 gives the length of the sample in inches and tenths of an inch, ranging from 2.6 to 3 .6 inches, while dial I54 gives divisions of the length of the sample in thousandths of an inch, ranging from zero to .100. The gears I50 are disposed between and supported on two spaced, parallel plates I60 and IBI which are mounted on the partition member 89 in the space between the latter and the front wall 32 of the housing. Meshing with the other train of ge'arsin the gear assembly I50 is a small pinion I62 fixed to the end of the lower lead screw 9|, which drives the dials I53 and I54.

As best shown in Figure 6, the two dials I53, I54 are set into circular cavities formed in the outer surfaces of disks I63 and I64, and the faces of the dials are flush with the exposed outer surfaces of the annular rims of their respective disks. These exposed rims of the disks I63, I64 constitute the index rings I55, I55 mentioned earlier, and suitable index marks are provided thereon which cooperate with the markings of the dials to give the instrument readings. The disks I63, I64 are mounted on tubular shafts I65 and I66, respectively, which are operatively connected with the first-mentioned train of gears in the assembly I50, and are rotated by the surcharge adjustment knob I44 when the latter is turned. The dials I53, I54 are mounted on shafts I81 and I68, respectively, which pass through the centers of tubular shafts I65, I66, and are operatively connected with the lastmentioned train of gears in the assembly I50, so that the said dials are driven by the lead screw 9|. Thus, when the surcharge adjustment knob I44 is turned, two functions are performed: first, the screw I32 is advanced through the screw plate 99 so that its inner end is positioned to engage the cover plate of the limit switch box I20 and actuate the microswitches contained therein when the springs I03 and I04 have been compressed to a predetermined deflection; and second, the dials I5I, I52 are turned to show the surcharge pressure which will be exerted on the sample when the surcharge mechanism 40 comes to rest, while simultaneously, the index rings I55, I56 are turned to positions which will indicate on their respective dials I53, I54 the actual length of the sample under the surcharge pressure obtained when the surcharge mechanism comes to a stop for the first time.

The cooperative relationship between the adjustment screw I32 and the surcharge pressure dials II, I52 is based upon the well-known fact that the deflection of a spring is directly proportional to the force exerted thereon. Since they are geared directly to screw shaft I32, dials I 5I, I 52 actually give a reading based upon the number of turns made by the screw shaft in screw plate 99, which, in turn, determines the distance from the plate 99 to the end of the screw shaft I32. The farther the screw shaft projects beyond the screw plate 99, the less clearance there will be between the end of the screw shaft and the cover plate I23 of the limit switch box, and the less deflection there will be in the springs I03, I04 when the shear mechanism comes to a stop. Thus, the surcharge pressure, which is a function of the spring deflection, depends upon the position of the end of screw shaft I32 with respect to the cover plate I23 when the springs I03, I04 are unstressed, and the dials I5I, I52 are merely calibrated to show the spring pressure that will be obtained for any given position of the screw shaft.

As mentioned earlier, the dials I 53, I54 are geared to the lead screw 9I which, together with lead screw 90, causes the screw plates 99, I00 to move together or apart, depending upon the direction of rotation. The position of the dials is, therefore, directly related at all times to the d stance between the two screw plates. In measuring the length of the sample from the distance between the screw plates, it is necessary, of course, to take into account the amount of deflection of the springs I03, I04. This is done by gearing the index rings I55, I56 to the surcharge adjustment knob so that the position of the index rings is directly related to the spring deflection, or surcharge pressure. Thus, the readings obtained from the positions of the reference points on index rings I55, I56 with respect to the calibrations on dials I53, I54 represent the distance between the screw plates 99, I 08, from which has been subtracted the variable distance between each of the screw plates and its associated spring plate 86, with suitabl allowance being made for the constant distance between each of the spring plates and the outer face of its corresponding stone disk 80.

The spring plates 86 and screw plates 99, I03 are prevented from over-traveling their normal limits by means of three microswitches I69, I10 and HI that are mounted on a supporting bracket shelf I12 which is fixed to the partition member 46. Microswitch IE9 is normally open, and is operatively connected to the coil of the impulse relay I I1 which energizes one or the other of relays II8 and H9 controlling the forward and reverse circuits, respectively, of the surcharge motor I06. When microswitch IE9 is open, relay H1 is normally operative to transmit current from one of its poles to the coil of relay H8, thereby energizing the latter. This completes the forward drive circuit to the motor I96 and causes the latter to run in the forward direction. If the left hand spring plate 86 over-travels its limiting position, the operating plunger of microswitch I69 is engaged and depressed by a bar I13 fixed to the spring plate, which closes the switch and energizes relay II1. This has the effect of opening the circuit to relay H8 and closing the circuit to relay II9, which causes the motor I06 to stop running in the forward direction and start up in reverse, so that the spring plate 86 is backed away from its past-limit position.

Both of the microswitches I10 and HI are normally closed, and function to limit the reverse travel of th screw plate 99. These switches are connected together in series, and are operatively connected to relay II 9 controlling the reverse drive circuit to motor I06. If either switch is opened, relay I I9 is disabled, causing the motor to stop running in reverse. Switch I19 has a roller carried at the end of an actuating lever arm, and when the said roller is engaged and lifted by a block I14 on the screw plat 99, as shown in Figure 8, the contacts in the switch are opened. Switch I H has an operating plunger that is engaged directly by the block I14 when the screw plate 99 has traveled a short distance beyond the point at which switch I19 was actuated.

With the machine operating under its automatic controls, the motor I96 is stopped when switch I10 is actuated. However, there ar occasions when it may be necessary to back the screw plate 99 still further, and to this end, a manually controlled reverse switch I15R (see Figure 21) is connected into the line between switch Ill and switch I10, so that the motor I06 can be run in reverse even though the switch I 10 is open. With the opening of switch I1I, the reverse circuit of the motor I06 is finally broken completely, and cannot be restored until the screw plates 99, I99 have been run forwardly to disengage one or both of the limit switches I19, Ill.

The shear mechanism 4 I, as mentioned earlier, is contained within a floating shear box 42 which is seen to comprise a bottom panel I 16, side walls I11 and I18, top panel I19, and end walls I90 and I8I. The shear box is disposed between vertical partition members 46 and I 82, the latter being parallel to and spaced to the left of member 46 and extending from the front wall 32 of the housing to the rear wall 33 thereof. Floating support for translational movement of the shear box 42 is provided by two ball bearing mounts I83 at opposite sides thereof, each of said mounts comprising a horizontally extending center bar I84 of generally rectangular cross-section disposed between parallel upper and lower bars I85 and I86, respectively. The ends of the center bar I84 are machined down to form cylindrical studs I81 which pass through holes I88 in the members 46 and I82, and which are threaded to receive nuts I89. Formed in the top and bottom edges of the center bar I84 are races I99 that cooperate with races I9I in the top and bottom members I 85, I86 to receive ball bearings I 92. The top and bottom members I85, I86 of the mount are secured by screws I93 to the side walls I11 and I18, of the shear box 42 so that the latter is thus supported on the ball bearings I92 and rolls freely thereon along the length of the races I99, l9I. The maximum movement of the shear box is limited, of course, to the sum of the clearances between the ends of the box and the partition members 46, I82; although the actual movement of the box during the performance of a test is usually only a small fraction. of an inch.

Shearing of the soil sample 50 is performed by a screw shaft 200 which extends through and is slidable within a bushing 20I mounted on the end wall I8I of the shear box 42. The projecting outer end of the screw shaft 290 is connected to the center holder 56 by a swivel connection 202 which transmits the pull to the holder without torsion. The swivel connection 202 is essentially a double row thrust bearing consisting of two 

